We begin this hour in Florida, where the Republican presidential candidates are busy preparing for yet another nationally televised debate this evening and what a difference a week makes. Over the weekend, former Speaker Newt Gingrich won a resounding victory in South Carolina. That win along with a revised vote total in Iowa that put former Senator Rick Santorum on top there, dealt a big blow to former Massachusetts Governor Mitt Romney's campaign.

Two weeks ago, Romney won the New Hampshire primary easily and seemed to have the GOP presidential nomination all but locked up. Well, in the last two days, Mitt Romney has responded by pounding Gingrich for his work consulting on health care issues and on behalf of Freddie Mac.

MITT ROMNEY: If you're working for a company, getting paid for a company through one of your many entities and then you're speaking with congressmen in a way that would help that company, that's lobbying. If it walks like a duck and quacks like a duck, it is a duck.

BLOCK: And here's Newt Gingrich responding to that critique this morning on ABC's "Good Morning America."

NEWT GINGRICH: I did no lobbying, period. He keeps using the word lobbyist because I'm sure his consultants tell him it scores well. It's not true. He knows it's not true. He's deliberately saying things he knows are false.

BLOCK: Well, joining us to talk about the race and tonight's debate is NPR's national political correspondent, Mara Liasson who is in Tampa. And, Mara, let's start with Newt Gingrich who got a huge boost out of a series of strong debate performances in that South Carolina primary. Do you expect Newt Gingrich again to be on the attack this evening?

MARA LIASSON, BYLINE: Yes, I do. He'll be on the attack against Mitt Romney. He'll also be on the attack against establishment elites. That worked very well for him in South Carolina, despite the fact that he has been in Washington for 33 or 40 years, according to Mitt Romney's math. He is known as an anti-establishment bomb thrower. That's his persona. I think the challenge for Gingrich in Florida is to see if he can use his momentum and his authenticity against Romney's obvious financial and organizational advantages here.

BLOCK: We mentioned, Mara, that Mitt Romney has been pounding Newt Gingrich for his work with Freddie Mac, went so far today as to say: You should give back the money that Freddie Mac paid you. Any sign that that line of critique is working with voters?

LIASSON: Not yet. The average of the polls in Florida still show Gingrich almost 10 points above Romney. Now, Romney has been able to kill that kind of a Gingrich surge before by spending millions of dollars in negative ads against him. It might work again. He's certainly going to try it in Florida. But I do think that this attack on Gingrich's work for Freddie Mac is probably Romney's best hope, because Freddie Mac is viewed by many conservatives in the Republican Party as the number one cause of the financial crisis.

The test for Romney is to see also if he can neutralize Gingrich's advantages in the debate, see if he can get under Gingrich's skin and turn in a better debate performance himself.

BLOCK: Mara, another issue that Mitt Romney has been taking a drubbing for is his tax returns. And he has now said he will release at least some of those returns tomorrow. Do you think that will put that issue to rest?

LIASSON: I doubt it. I think that there'll be calls for him to release multiple years of returns, just like his father did when he ran for president. It's also going to raise the issue of tax policy. He said that he pays a 15 percent rate. Newt Gingrich has said, well, why doesn't he propose paying - that everyone should pay a 15 percent rate? Newt Gingrich has proposed an alternative flat tax that he is now calling the Romney tax, where everybody would have the choice of paying 15 percent. And I think that will open up a whole new debate about fairness and tax policy and tax reform.